Autonomic nervous system

Autonomic nervous system Dr. Maha Talal

THE NERVOUS SYSTEM
The nervous system is a complex part of the human body concerned with the regulation and coordination of body activities such as movement, digestion of food, sleep, and elimination of waste products. The nervous system has two main divisions: the central nervous system (CNS) and the peripheral nervous system (PNS).


Autonomic nervous system: The component of the NS ( Nervous System) that functions below the conscious level, controlling several physiological processes: 1. Distribution of blood flow & tissue perfusion 2. Regulation of blood pressure 3. Control of visceral smooth muscle ( bladder, bowels) 4. Control of endocrine and exocrine glands 5. Control of metabolic energy (glycolysis, glucogenesis etc)

Autonomic nervous system division to : 

Sympathetic or (adrenergic) (thoracolumber) Neurotransmitter: )epinephrine, norepnephrine) Receptor : α1 , α2 , β1, β22. Parasympathetic or (cholinergic): (craniosacral) Neurotransmitter :(acetylcholine)Receptors: M1, M2 , N1, N2

NEURONAL INNERVATION TO ORGANS

Classify of autonomic nervous system 1.release of n.t 2.on structure 3.from origin 4.according to the receptor

INNERVATION AT MOST SITES

Functionally, the two are generally antagonistic. The sympathetic division stimulates functions involved in “fight or flight” reactions (fear, anger, etc), whereas the parasympathetic division stimulates more tranquil functions (“rest-and-digest”).

Neurotransmitters are chemical substances called neurohormones. These are released at the nerve endings that facilitate the transmission of nerve impulses.

Norepinephrine (mainly) and epinephrine (in adrenal gland) released at the postganglionic sympathetic neuron . These neurons are also called ‘Adrenergic’..


Cholinergic Nervous System: Acetylcholine neurotransmitter releasing nerve fibers (parasympathetic). Acetylcholine is the preganglionic neurotransmitter in the sympathetic system. A few sympathetic (sweat glands and salivary glands) have Acetylcholine as the postganglionic neurotransmitter

Parasympathetic Nervous System

Parasympathetic:
The parasympathetic nervous system helps conserve body energy and is partly responsible for such activities as slowing the heart rate, digesting food, and eliminating body wastes. The ganglia are usually close to or embedded in the target organ. Acetylcholine is both preganglionic and postganglionic neurotransmitter (Cholinergic).

Biologic responses to parasympathetic stimulation:Constriction of pupil (miosis), ciliary body (“accommodation” of lens)Contraction of smooth muscle in the GI (“peristalsis”) and urinary tractConstriction of the bronchioles (“bronchoconstriction”)Slowing of heart rate (“bradycardia”)Increased secretion by the glands

 Acetylcholine release in cholinergic neuron involve 6 steps :

Synthesis of Ach Storage of Ach in vesicles Release of Ach Binding to receptor Degradation of Ach Recycling of choline

AGENTS AFFECTING CHOLINERGIC TRANSMISSION

Hemicholinium Latrotoxin Vesamicol Botulinus toxin Calcium Physostigmine Atropine d-Tubocurarine

DRUG ACTING ON A.N.S

1- cholinergic drugs A- Parasympathomimetic D B- Parasympathlytic D 2- adrenergic drugs A- sympathomimetic D B- sympatholytic D

Parasympathetic drugs : 

A- Parasympathomimetic DCholinergic agonist: Agents that bind to acetylcholine receptors and stimulates the parasympathetic system (“parasympathomimetic”).B- parasympathlytic DCholinergic antagonist: Agents that bind to acetylcholine receptors but exhibit no intrinsic activity (“parasympatholytic” – competitive to endogenous Ach)

Parasympathomimetic drug:

1- direct acting cholinergic agent 2- Indirect acting cholinergic agent: divided into reversible & irreversible

Parasymathomimetic drug

direct
Cholin esterase
Naturally occurrence alkaloid

A- cholin esterase1-Acetylcholine

Prototypical muscarinic (and nicotinic) agonist, Nonselective action. poor therapeutic agent. Chemical/enzymatic instability; Low bioavailability (poorly absorbed); Quick onset and short duration of action. Use: In ocular surgery, causes complete miosis in seconds.


Effect of ACH : 1.on the intestine : Increase S.M contraction 2.on the urinary tract : Increase in muscle tone and contraction 3. on blood vessels : vasodilatation

4.on the secretary gland :increase secretion 5. on the S.M of trachea :contract , increase bronchial secretion, bronchoconstriction , 6.on the skeletal Muscle : increase Muscle tone 7. On the heart : bradycardia 8. On the eye : miosis , decrease in I.O.P 9 .On the adrenal gland